Detection of two smooth colony phenotypes in a Salmonella enteritidis isolate which vary in their ability to contaminate eggs.

Salmonella enteritidis isolates were obtained from eggs after infection of Leghorn hens with a parent isolate (SE6) known to only infrequently contaminate eggs. Isolates from eggs exhibited two phenotypes that were subtly different. One phenotype was typically smooth, while the other was transiently rough. Both sets of isolates were phage type 13A and positive for D1 epitopes. Immunoblot analysis of entire colonies and gas chromatographic analysis of purified lipopolysaccharide revealed that the phenotypic difference between isolates was due to a quantitative difference in O antigen and possibly a qualitative difference in the lipid A core region. In addition, the two isolates had different opacity properties when examined at 600 nm. When the two isolates were used to inject egg-laying hens, a significant difference in the ability to contaminate eggs was detected.